The present invention relates to an automatic wire electrode feeder of a wire electric discharge machine for machining a workpiece by electric discharge energy when an electric discharge is generated between the traveling wire electrode and the workpiece.
In the case of machining a workpiece by a wire electric discharge machine, in general, in the initial stage of electric discharge machining, while a wire electrode, which will be referred to as a wire hereinafter, is being inserted into an initial hole, electric discharge machining is started, and the wire is cut off at the end of electric discharge machining, and then the process proceeds to a position at which machining of the next profile is started. Accordingly, in order to automatize electric discharge machining, it is necessary to automatize the processes of inserting the wire into the initial hole and connecting the wire, and further it is necessary to automatize the processes of cutting off and recovering the wire. Therefore, in order to automatize the above processes, the technique of an automatic wire feeder, in which the wire is automatically connected and cut off, has been conventionally put into practical use.
In this connection, when the wire is automatically connected, an end of the wire, which has been cut off, is automatically sent out by a motor and others, and it is necessary for the wire to be inserted into small portions which are provided in: the inserting passage such as an upper and a lower guide for supporting the wire on the upper and lower sides; an upper and a lower electric contact piece for supplying an electric discharge machining current to the wire, an initial hole formed in the workpiece; and a recovery mechanism for recovering the workpiece. Therefore, when the wire is given a heavy frictional load in each portion described above in the process of automatic wire connection, or when the wire is caught by each portion described above, it is impossible for the wire to be smoothly inserted, and a portion of the wire is buckled up in the wire inserting passage. When the wire is buckled up in this way and the feeding of the wire is continued, the wire is forced out from the inserting passage at the buckling position, and the feeding of the wire end portion is stopped and the wire connecting motion is completely stopped.
In order to cope with this situation, Japanese Unexamined Patent Publication No. 01-274926 discloses a technique, which is described as follows. When it is detected that the wire electrode is not engaged with the wire recovery device in the process of automatic feeding of the wire, the process is returned to the initial stage. When it is detected that the process has been returned to the initial stage, a command to feed the wire again is given so as to start wire feeding. According to this technique, when the frictional load is positively heavy or the wire is caught by the inserting passage, it is possible to connect the wire once more even after a failure of connecting it. However, this technique is disadvantageous as follows. Since it takes time for the wire to be engaged with the wire recovery device, the detection time is extended. Further, since the process must be returned to the initial stage each time, the entire process time from the detection of failure of connecting the wire to the success of connecting the wire is greatly extended.
Further, when the buckled portion is located at a position lower than the cutting mechanism, it is possible to restore the machine to its original state by cutting and removing this buckled portion. However, when the buckled portion is located at a position higher than the cutting mechanism, it is impossible to remove this buckled portion, that is, it is difficult to automatically restore the machine to its original state. Unless the above problems are solved, operation of the machine is completely stopped.
On the other hand, Japanese Unexamined Patent Publication No. 02-160422 discloses the following technique. In an upper portion of the wire guide pipe, there is provided a buckling detecting member having a passage made of conductive material, the diameter of which is large. Also, there is provided a buckling detecting circuit for detecting a change in voltage impressed between the buckling detecting member and the electric contact piece of the upper guide block. When buckling of the wire is detected, the wire is rewound to the initial state and the wire connecting work is repeated. However, in the case where buckling is electrically detected as described above, the buckled portion must be specified by the detecting section, which is disadvantageous. Further, in order to increase the sensitivity of detection, it is necessary to decrease clearance between the electric contact section and the wire as small as possible. When the clearance of the detecting section is decreased, it becomes difficult for buckling to be caused in this portion, and buckling is caused in other open portions, which is an incompatible problem.
Further, Japanese Unexamined Patent Publication No. 62-162425 discloses a technique which will be described as follows. A deviation of the wire from a predetermined passage is detected by an optical sensor, and a wire draw-back means is operated so as to draw the wire by a predetermined length so that looseness of the wire can be removed, and the automatic wire connection is started again. However, this technique is disadvantageous as follows. In order to positively remove looseness of the wire, it is necessary to provide a mechanism capable of being used as a wire draw-back means. Further, when looseness of the wire can not be completely removed by the above wire draw-back means, it is necessary to execute the wire winding motion by the feed motor. Therefore, it takes long time to start automatic wire connection again.
Accordingly, in order to prevent buckling of the wire caused in the wire inserting passage in the process of automatic wire connection and in order to realize a quick automatic wire connection even if the wire is given a load in the inserting passage, it is necessary to provide a large open space in the wire inserting passage and use a sensor, the detecting sensitivity of which is high, and it is also necessary to positively and quickly conduct a feeding and rewinding motion of the wire by the feed motor. However, when the feeding and the rewinding motion of the wire are continuously conducted, the wire is vibrated. Accordingly, it is necessary to instantaneously distinguish between a state of deflection of the wire in the wire inserting passage and a state of vibration of the wire, the deflection of which is small.
The present invention has been accomplished to solve the above problems. It is an object of the present invention to positively detect the occurrence of buckling caused by an inserting load when a wire is automatically connected. It is another object of the present invention to reduce the time necessary for reconnecting the wire and enhance the reliability.
An automatic wire feeder of a wire electric discharge machine of the first invention comprises: an optical sensor for detecting positional information of a wire electrode in an inserting passage between a feed roller for feeding a wire electrode and an upper wire guide; and a control unit for discriminating a state of vibration or deflection of the wire electrode according to the positional information detected by the optical sensor and also for controlling a feeding and rewinding motion of the feed roller according to a quantity of deflection of the wire electrode.
An automatic wire feeder of a wire electric discharge machine of the second invention comprises a control unit, wherein the control unit stops a feeding motion of the feed roller when the quantity of deflection of the wire electrode is increased by a predetermined quantity in the feeding motion of the feed roller, the control unit starts rewinding after a predetermined period of time, the control unit stops rewinding when the quantity of deflection of the wire electrode is decreased by a predetermined quantity in the rewinding motion, and the control unit starts feeding the wire electrode after a predetermined period of time.
An automatic wire feeder of a wire electric discharge machine of the third invention comprises a rate changeover means, wherein the rate changeover means reduces a feeding rate of the feed roller according to the number of times of execution of the rewinding motion.
An automatic wire feeder of a wire electric discharge machine of the fourth invention is characterized in that a direction in which the directivity of the optical sensor is narrow is made to agree with a direction of the normal line of the surface of the pinch roller and capstan roller for feeding the wire electrode.